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Session 31 - Quasars.
Oral session, Wednesday, January 07
International Ballroom East,
We investigate the relations between emission line strengths and widths and observed continuum properties of low redshift (z < 1) quasars for which IR-soft-X-ray spectral energy distributions (SEDs) are available. This includes the correlations between optical and UV lines with both the luminosity and the shape of the quasars' continuum, as well as correlations between the lines. Our sample consists of 41 objects (half of them being radio-loud), which have Einstein X-ray observations with sufficient counts to define the X-ray shape.
We find the equivalent-width (EW) anticorrelations with UV luminosities (the Baldwin effect) for the Ly\alpha, H\beta lines and a marginal anticorrelation for CIII]. We do not find a Baldwin effect for the CIV line, however the exclusion of narrow line low luminosity AGN reveals a significant correlation. Anticorrelations with \alpha_ox are also found: highly significant for EW(CIV) and less significant for EW of H\beta, OVI and Ly\alpha lines. We find no correlations between the lines and X-ray luminosity or X-ray slope. The FeII optical multiplet shows no simple relationship with luminosity or continuum slope, however there is a tendency for objects with flat X-ray spectra and/or strong X-ray luminosities not to have strong FeII.
Our data do not favor a model in which changes in continuum shape (due to e.g., a decreasing ionization parameter) cause the Baldwin effect. The data can be explained with a model where limb darkening and projected surface area of an optically thick, geometrically thin disk result in a viewing-angle dependent UV apparent luminosity and an angle independent X-ray luminosity. The scatter in our correlations is larger than expected from the disk model, possibly indicating the existence of dust which reddens the central engine as well as the BLR lines.
